FIELD OF THE INVENTION
The invention relates to a method for detecting the position of stacked flat material, in particular of a paper pile on a feeder of a printing machine, wherein at least one light beam is directed onto the side of the pile, is reflected therefrom and evaluated as a measure of the position.
The invention also relates to a device for performing the method, having a spacing sensor, with at least one light source and at least one receiver for the reflected light, and an evaluation device.
In the processing of paper sheets, and in particular in the feeder of printing machines, but also in the further processing of printed sheets, or in other cases of processing stacked material such as cardboard, the position of the stack or pile has to be detected. This is necessary in order to allow automatic processing, in particular, in order to remove sheets from the top surface of the pile and to feed those sheets to a printing, cutting, binding or other machine. For this purpose, it is necessary for both the lateral alignment and the vertical alignment of the pile to be detected. With regard to the lateral alignment, it is usually sufficient to detect the position of the side that extends parallel to the transport path of the material. Vertical alignment is necessary for gripping the uppermost stacked material by an appropriate device.
In the case of printing machines, vertical alignment is particularly important for the feeder pile because the suction head for removing the uppermost sheet and an underblowing device for blowing beneath the sheet have to be adjusted to the pile height. At the feeder of a printing machine, lateral alignment of the removed sheet at side lays can take place usually only in a small region. The transfer to the first gripper bar must, however, take place with extreme precision. Heretofore, it has been customary, for detecting the position of the pile, to provide separate sensors for the side and height detection, for which mostly ultrasonic sensors have been used.
The published German Patent Document DE 41 29 702 C2 discloses a method and a device for pile-side detection, the pile side being detected with the aid of a light beam reflected thereon, and the position of the pile side being determined in accordance with the trianguation principle. In this regard, however, a sensor is used only for detecting the pile side and not the top edge of the pile. A second sensor would have to be provided for this purpose, but this is complex and expensive.